1. Technical Field
The present invention relates to a method of forming a toner image and an electrophotographic image forming apparatus including a toner, and more particularly, to a method of forming a toner image and an electrophotographic image forming apparatus including a toner, capable of realizing a wide color gamut.
2. Background Art
In image forming apparatuses such as laser printers, photocopiers, and multifunction devices, toner particle size needs to be decreased and a color gamut needs to be increased to speed up operations of the image forming apparatuses, fix toner images at low temperature, and to form high-resolution images. In this regard, the color gamut may be determined by lightness (L), redness (a), and yellowness (b) displayed in color coordinates. That is, if ‘a’ is a negative value, a green color gamut is obtained, and if ‘a’ is a positive value, a red color gamut is obtained. If ‘b’ is a negative value, a blue color gamut is obtained, and if ‘b’ is a positive value, a yellow color gamut is obtained.
A method of developing toner is classified into a two-component developing method using toner and carriers, and a one-component developing method using toner only.
Meanwhile, as the price of personal computers (PCs) decreases with the development of information-communication and media technology, the number of PCs in use has become increased. Accordingly, the number of laser printers as well as inkjet printers for professional and personal use has also become increased. Thus, image forming apparatuses employing the one-component developing method, which are suitable for small-sized and low-priced laser printers, have become more important.
In general, toner is prepared by mixing a thermoplastic resin as a binder resin, with a colorant, a charge control agent, a release agent, or the like. In order to improve physical properties such as fluidity, charge controlling properties, or cleaning properties of toner, fine particles of inorganic metal such as hydrophobic silica and titanium oxide; fluorinated polymer particles; or poly(methyl methacrylate) (PMMA) particles may further be added to the toner as external additives.
Color of toner images may vary according to functions of materials added into toner that is an electrophotographic developer. A toner image may have a natural color by using toner having a wide color gamut.
U.S. Pat. No. 6,203,957 discloses spherical toner particles using a colorant. The toner using only a colorant has excellent lightfastness but a narrow color gamut.
Japanese Patent Publication No. 2003-34765 discloses a color inkjet ink set using dyes. The dyes used in the ink are water-soluble dyes, and the inks are classified into a magenta ink, a yellow ink, a cyan ink, an orange ink, a green ink, and a violet ink according to the color of the dyes. The ink set may form images having an excellent color gamut. However, the ink set has poor lightfastness due to the dyes.
European Patent No. 0915386 discloses a method of polymerizing toner by preparing polymer resin particles using seed polymerization or dispersion polymerization, and dispersing the polymer resin particles and dyes in a solvent. However, since dyes are used for the polymerization of toner, the toner has poor lightfastness despite a high image density and wide color gamut.